Isobaric Molar Heat Capacities Research Articles

Thermodynamic Stability of Fenclorim and Clopyralid.

The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (p,T) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.

Effect of Cross-Linking Density on Horizontal and Vertical Shift Factors in Linear Viscoelastic Functions of Epoxy Resins

Epoxy resins are an important class of thermosetting resins, and their network structure, obtained by the curing reaction of epoxy and amine compounds, plays an important role in the material properties. We here revisited a time–temperature superposition (TTS) principle applied to the dynamic viscoelastic functions of epoxy resins, in which the network was well defined and systematically varied on the basis of the length of n-alkyl diamine. The superimposition of isothermal curves in the frequency domain required not only a horizontal shift but also a vertical shift, regardless of the length of n-alkyl diamine. The temperature dependence of the horizontal shift factor, aT, could be well expressed by the Williams–Landel–Ferry equation. The fitting parameter, called C2, increased with decreasing alkyl chain length of the diamine, meaning that the thermal expansion of the free volume was suppressed due to greater cross-linking density. This was qualitatively confirmed by a full-atomistic molecular dynamics (MD) simulation. Meanwhile, the vertical shift factor, bT, increased with increasing temperature, and the extent was smaller with increasing cross-linking density. This can be explained in terms of the entropic contribution to the modulus in the temperature region above the glass transition temperature. The entropy change estimated using the isobaric molar heat capacity from the MD simulation strongly supported this hypothesis. The knowledge here obtained should be useful for a better design of thermosetting polymers as well as for the prediction of long-term durability.

Volumetric properties of binary mixtures of tetrahydrofuran, dimethyl adipate, 1-butanol and 2-butanol from (288.15 to 323.15) K and modeling by Prigogine-Flory-Patterson (PFP) and Extended Real Association Solution (ERAS) models

In this work, experimental densities data of the binary system tetrahydrofuran + 2-butanol have been determined at eight temperatures, T=(288.15–323.15) K and atmospheric pressure and used for excess molar volume calculations. Also, partial molar volumes, excess partial molar volumes and partial molar volumes at infinite dilutions were calculated for further non-ideal behaviour of binary mixture. Excess molar volume, VE, of experimental determined system tetrahydrofuran + 2-butanol, and four previously published binary systems, tetrahydrofuran + 1-butanol, dimethyl adipate + 1-butanol, dimethyl adipate + 2-butanol and dimethyl adipate + tetrahydrofuran were correlated with two models, Prigogine-Flory-Patterson (PFP) and Extended Real Association Solution (ERAS). In order to apply the proposed models additional data of ultrasonic speed of sounds for pure components, dimethyl adipate, tetrahydrofuran, 1-butanol and 2-butanol, were measured in the temperature range T=(288.15–323.15) K and at atmospheric pressure. Volumetric coefficients, thermal expansion coefficient α and isothermal compressibility κ were calculated from density, ultrasonic speed of sound and isobaric heat capacity data. Isobaric molar heat capacities Cp,m at all temperatures for all pure components were obtained by correlation of literature data.Both models, PFP and ERAS were used for analysis of molecular interactions present in the investigated solutions.

JPCRD: 50 Years of Providing the Scientific Community with Critically Evaluated Thermodynamic Data, Predictive Methods, and Large Thermodynamic Data Compilations

A brief overview is provided on articles published in the Journal of Physical and Chemical Reference Data containing experimental thermodynamic data as well as group contribution methods used to predict thermodynamic quantities of organic compounds. Published papers have contained large compilations of experimental and calculated condensed-phase and gas-phase standard molar enthalpies of formation, isobaric molar heat capacities, molar enthalpies of fusion, molar enthalpies of sublimation, and molar enthalpies of vaporization.

Densities, heat capacities, viscosities, 1H- and 13C-NMR spectra, and solvatochromic parameters of binary mixtures of 1,3-dimethyl-1,3-diazinan-2-one (DMPU) and water

The compound 1,3-dimethyl-1,3-diazinan-2-one (N,N’-dimethylpropyleneurea, DMPU) is a dipolar aprotic solvent with very strong electron-donating abilities but which is much less toxic and less carcinogenic than similar solvents such as the widely used HMPA (hexamethylphosphorictriamide). This paper reports densities and viscosities of the binary mixtures of (DMPU + water) in the temperature range (293.15 to 353.15) K at 5 K intervals, over the whole composition range. Isobaric heat capacities of these mixtures were measured by flow calorimetry at 298.15 K. The 1H- and 13C-NMR spectra as well as the solvatochromic parameters (polarizability, π*, hydrogen-bond acceptor basicity, β, and hydrogen-bond donor acidity, α) of the mixtures were also determined. The densities and viscosities were sensitive to traces of water in the organic-rich region while the heat capacities were not. Excess molar volumes were strongly negative, showing an extremum at mole fraction xDMPU ≈ 0.40. The variation of viscosity with mixture composition was similar to the density with a sharp maximum at xDMPU ≈ 0.35. Apparent molar volumes, Vϕ, of the mixtures show that the water-DMPU interactions have a larger effect on Vϕ of water than on DMPU. While the standard isobaric molar heat capacity of DMPU in water is much higher than that of DMPU itself, the corresponding value for water in DMPU was not much influenced by the presence of DMPU. The 1H-NMR spectra show that the chemical shift of the water protons is more influenced by mixture composition than those of the DMPU protons. A de-shielding of the DMPU carbonyl carbon resonance was observed in the 13C-NMR spectra at low xDMPU, indicative of H-bonding between the water protons and the non-bonding electrons of the carbonyl oxygen.

Thermophysical Properties of Mixtures of Titanium(IV) Isopropoxide (TTIP) and 2-Propanol (iPOH)

The present work provides thermophysical data on binary mixtures of titanium(IV) isopropoxide (TTIP) and 2-propanol (iPOH), which are important precursor solutions in spray flame synthesis of nanoparticles. The specific density, viscosity, thermal conductivity, and molar isobaric heat capacity were measured at 101.3 kPa and temperatures ranging from 293.15 to 333.15 K. The vapor–liquid equilibrium (VLE) was measured at pressures ranging from 20 to 80 kPa. Furthermore, self-diffusion coefficients of pure iPOH were measured at 101.3 kPa and temperatures ranging from 293.15 to 333.15 K. A qualitative study using 1H NMR spectroscopy provides evidence for a cross-association between TTIP and iPOH in the mixture. Correlations for all studied thermophysical properties are provided. The results establish a rational basis for the design of spray flame synthesis processes.

Thermodynamic properties of metaschoepite predicted from density functional perturbation theory

Density functional perturbation theory (DFPT) calculations of the thermodynamic properties of metaschoepite, (UO2)8O2(OH)12·10H2O, are reported. Using a recently revised crystal structure of metaschoepite, the predicted molar entropy and isobaric heat capacity are overall significantly smaller than previous calculations using an earlier orthorhombic crystal structure model. The present DFPT calculations also show large differences between the thermodynamic functions of metaschoepite and schoepite, which might reflect the change in phonon properties upon removal of two H2O molecules per formula unit and alteration of the H-bonded interlayer water network from schoepite to metaschoepite.

Relationship between Heat Capacity and Topological Characteristics of Molecules in a Series of Gaseous Substituted Derivatives of Alkenes at a Pressure of 100 kPa and in the Temperature Range from 298.15 to 1000 K

A structure–property multivariate nonlinear model for calculating the isobaric molar heat capacity of alkenes in the gas phase is proposed. The inclusion of topological descriptors, such as the Wiener index, Randich index, topological matrix eigenvalues, etc., as well as an index that takes into account the cis and trans isomers of alkenes, is a feature of this model. The resulting model adequately describes the specific heat of hydrocarbons with more than three carbon atoms. A relevant algorithm for calculating the molar heat capacity is developed. The proposed model can be used in chemical engineering and the technological design calculations of chemical reactors and petrochemical plants.

Thermal properties of novel oligoether-substituted ionic liquids and the influence of alkyl-substituent isomery

This paper is a continuation of a study focused on thermodynamic properties of isomeric and quasi-isomeric ionic liquids. In this work 5 novel ionic liquids were synthesized, namely 1-(2-(2-ethoxyethoxy)ethyl)-3-alkylimidazolium bis(trifluoromethylsulfonyl)imides, where alkyl stands for different C5 substituents. These species were characterized as to their isobaric molar heat capacity and thermal stability. The results are discussed with respect to different substituent isomerism and compared with data from our previous work (Rotrekl, Fluid Phase Equilib. 2017) that reported on a similar group of isomeric ionic liquids, namely 1-butyl-3-alkylimidazolium bis(trifluoromethylsulfonyl)imides. Data analysis of the experimental heat capacites was carried out using a non-statistical approach of the mathematical gnostics. The conclusions drawn from the present work bring an insight into the fine structure-property relationship which is useful in the development of predictive tools as well as it direct applications such as in energy storage or thermal fluids development.

A comprehensive study of the thermophysical properties of reline and hydrated reline

In this work, a physicochemical characterization of the Deep Eutectic Solvent, reline (formed by chloline chloride and urea in a molar ratio 1:2) and one of its aqueous mixtures (xreline = 0.645) has been made at atmospheric pressure (0.1 MPa) in a wide range of temperatures (288.15–338.15) K for reline and (278.15–338.15) K for the aqueous mixture. The measured properties were: density, speed of sound, refractive index, isobaric molar heat capacity, surface tension, kinematic and dynamic viscosity and electrical conductivity. Additionally, from these experimental results, some derivate properties such as isobaric thermal expansibility, isentropic compressibility, molar refraction, free volume and entropy and enthalpy of surface formation have been obtained. Taking into account the observed behaviour the introduction of water, at the considered composition, only modify drastically the dynamic viscosity and electrical conductivity.

Thermophysical Properties of Mixtures of Titanium(IV) Isopropoxide (TTIP) and p-Xylene

Titanium(IV) isopropoxide (TTIP) is an important precursor for the production of nanoparticles by spray flame processes. In these processes, the precursor is provided in a solution in a combustible solvent, which is p-xylene here. As no thermophysical data for solutions of TTIP in p-xylene were available in the literature, they were measured in the present work. The vapor–liquid equilibrium was measured at pressures ranging from 20 to 80 kPa. The specific density, viscosity, thermal conductivity, molar isobaric heat capacity, and self-diffusion coefficients were determined experimentally at 101.3 kPa at temperatures between 293.15 and 373.15 K. Sample compositions cover the range from pure TTIP to pure p-xylene. Chemical reactions in the studied system were considered. The experiments were carried out in such a way that they do not compromise the results for the thermophysical properties. The vapor–liquid equilibrium data were correlated using the NRTL model. Empirical correlations were established for the other properties. The results provide a rational basis for spray flame process design.

Experimental Study on Isobaric Molar Heat Capacities of a Deep Eutectic Solvent: Choline Chloride + Ethylene Glycol

In this study, a flow calorimeter is used to measure the isobaric molar heat capacities (Cp) of one deep eutectic solvent (DES) containing choline chloride and ethylene glycol at different molar ratios. The experiment is performed at temperatures from 313 to 343 K and pressures up to 25 MPa, while the expanded uncertainties of temperature, pressure, molar fraction, and Cp are estimated to be lower than 0.02 K, 5.0 kPa, 1.4 × 10–4, and 1.28%, respectively. The results show that Cp change linearly with temperature, while it is almost constant with a variety of pressure. A quadratic relation between Cp and molar fraction of ethylene glycol is observed, which shows a decreasing tendency with the increase of molar fraction. A correlation for the Cp of the chosen DES and pure ethylene glycol is proposed for a better application of the data.

Speed of sound for three binary (CH4 + H2) mixtures from p = (0.5 up to 20) MPa at T = (273.16 to 375) K

Speed of sound is one of the thermodynamic properties that can be measured with least uncertainty and is of great interest in developing equations of state. Moreover, accurate models are needed by the H2 industry to design the transport and storage stages of hydrogen blends in the natural gas network. This research aims to provide accurate data for (CH4 + H2) mixtures of nominal (5, 10, and 50) mol-% of hydrogen, in the p = (0.5 up to 20) MPa pressure range and with temperatures T = (273.16, 300, 325, 350, and 375) K. Using an acoustic spherical resonator, speed of sound was determined with an overall relative expanded (k = 2) uncertainty of 220 parts in 106 (0.022%). Data were compared to reference equations of state for natural gas-like mixtures, such as AGA8-DC92 and GERG-2008. Average absolute deviations below 0.095% and percentage deviations between 0.029% and up to 0.30%, respectively, were obtained. Additionally, results were fitted to the acoustic virial equation of state and adiabatic coefficients, molar isochoric heat capacities and molar isobaric heat capacities as perfect-gas, together with second and third acoustic virial coefficients were estimated. Density second virial coefficients were also obtained.

Thermophysical and volumetric properties of mixtures {carvacrol + ethanol} at several temperatures and atmospheric pressure

Experimental molar heat capacities at atmospheric pressure have been determined for the mixture {carvacrol + ethanol} every 10 K in the temperature interval (298.15–328.15) K and over the entire composition range with a Calvet type calorimeter. Densities, necessary for determining isobaric heat capacities, and ultrasonic speed of sound have been also measured at the same conditions. From these properties isobaric thermal expansivities, isentropic compressibilities, isothermal compressibilities, internal pressures and isochoric molar heat capacities have been calculated. Furthermore, in order to complete our thermophysical study the corresponding excess properties have been calculated and discussed in terms of molecular interactions. Finally, excess molar isobaric heat capacities have been calculated with COSMO-RS and compared to the experimental values.

Volumetric, acoustic and thermal properties of aqueous N,N-dimethylformamide system. Effect of temperature and composition

This paper presents the density (ρ), speed of sound (u) and isobaric specific heat capacity (cp) of an aqueous N,N-dimethylformamide (DMF) system. The measurements were performed over the entire composition range of (DMF + water) at four temperatures: 293.15, 298.15, 303.15 and 308.15 K. The density data was used to calculate the excess molar volume of the system (VmE), the partial molar volume of DMF Vm,2 and water Vm,1, as well as the molar expansion volume coefficient Ep,m. Based on the sound velocity and heat capacity values, it was possible to calculate the isobaric (Cp,m) and isochoric (CV,m) molar heat capacities, as well as the isentropic (κS) and isothermal compressibility (κT) coefficients and their molar counterparts (KS,m,KT,m). To study the structural changes in the examined system, excess molar functions Ep,mEKS,mEKT,mECp,mECV,mE were determined and the results were compared with ideal systems. Changes in the obtained values of the physicochemical parameters, as functions of composition and temperature, were analyzed in terms of the molecular interactions and structural differentiation of the investigated binary mixtures. The temperature effect exhibited a regular relationship with regard to the analyzed functions.

Equimolecular cocrystal of cis- and trans-coordinated N,N′-dimethylglycolurils: Some standard thermodynamic properties in the aqueous solution between 278.15 K and 318.15 K

In this paper, we have discussed the results of densimetric and calorimetric studies of dissolution process in water for the (1:1) cocrystal consisting of two heterocyclic isomers being cis- and trans-coordinated dimethylglycolurils (2,8-DMGU and 2,6-DMGU, respectively) in the temperature range from (278.15 to 318.15) K at the ambient pressure. The standard (apparent or partial at infinite dilution) molar volumes and isobaric expansibilities of cocrystal as a solute in water were derived from the experimental data on solution density. Using thermochemical measurements, the standard molar enthalpies and isobaric heat capacities of the dissolution of cocrystal in water were also determined at the temperatures of interest. Based on the previously obtained similar results for aqueous 2,6-DMGU and 2,8-DMGU, a comparative analysis of packing and interaction changes in the hydration complex induced by the cocrystallization process has been carried out. It was found that the formation of cocrystal leads to a peculiar “synergism” in both volume and heat capacity effect of N,N′-dimethylglycoluril hydration at all temperatures studied.

Thermophysical properties of choline and pyridinium based ionic liquids as advanced materials for energy applications

Phase transitions, isobaric heat capacities and thermal stability of four ionic liquids (ILs) are determined in this work. The selected Ionic Liquids (ILs) have two different cations, pyridinium and choline, and they are combined with three different anions, acetate, dihydrogen phosphate and tosylate. Solid-solid and solid-liquid phase transitions and isobaric molar heat capacities are determined using two calorimeters, both based on the differential scanning calorimetry methodology. Thermal stability of the studied compounds is analysed through the thermogravimetric technique (TGA). Degradation temperatures are obtained from TGA experiments using the dynamic method, whereas isothermal TGA is used to determine the maximum operation temperature. The results show that, all the ILs present crystalline behaviour, with melting temperatures within the interval of 88 °C and 123 °C, whereas heat capacities linearly increases with temperature. A clear dependence with the anion is observed for both heat capacities and thermal stability, being ILs with the tosylate anion those presenting the highest values of molar heat capacities and the highest thermal stability.

Approximating the Temperature–Entropy Saturation Curve of ORC Working Fluids From the Ideal Gas Isobaric Heat Capacity

Recently, we proposed an approximate expression for the liquid–vapor saturation curves of pure fluids in a temperature–entropy diagram that requires the use of parameters related to the molar heat capacity along the vapor branch of the saturation curve. In the present work, we establish a connection between these parameters and the ideal-gas isobaric molar heat capacity. The resulting new approximation yields good results for most working fluids in Organic Rankine Cycles, improving the previous approximation for very dry fluids. The ideal-gas isobaric molar heat capacity can be obtained from most Thermophysical Properties databases for a very large number of substances for which the present approximation scheme can be applied.

Effect of temperature and composition on the volumetric, acoustic and thermal properties of N,N-dimethylformamide + propan-1-ol mixture

The density (ρ), sound velocity (u) and specific heat capacity (cp) of a binary mixture of N,N-dimethylformamide and 1-propanol were measured over its entire composition range. The values of the obtained results were used to calculate the values of excess molar volume (VmE), molar expansion volume coefficient (Ep,m), molar isentropic (KS,m) and isothermal (KT,m) compressibility, isobaric (Cp,m) and isochoric (CV,m) molar heat capacity as well as their excess functions (Ep,mE,KS,mE,KT,mE,Cp,mE,CV,mE,uE). The analysis of changes in the physicochemical quantities was based on consideration us in an aspect of intermolecular interactions resulting changes in the mixture structure.

An experimental investigation and modelling of the thermal and caloric properties of nanofluids isopropyl alcohol - Al2O3 nanoparticles

An influence of Al2O3 nanoparticles on the thermodynamic properties of isopropyl alcohol in the liquid phase has been studied. Experimental measurements of the two-phase specific heat capacity have been performed in the temperature range from 184 to 340 K for samples with the mass fractions of the nanoparticles 0.0201, 0.0511 and 0.0996 kg·kg-1. The method of monotonic heating in an adiabatic calorimeter of variable temperature has been applied. The saturated vapor pressure of the nanofluids has been measured at the temperatures from 297 to 352 K and concentrations of the nanoparticles in isopropyl alcohol 0.0253, 0.0444, 0.0687, 0.0955 kg·kg-1. The results obtained have shown that the specific isobaric heat capacity of the nanofluids decreases up to 8.6% at 0.0996 kg·kg-1 of Al2O3 nanoparticles in comparison with pure isopropyl alcohol. In addition, the influence of Al2O3 nanoparticles on the specific enthalpy and specific entropy of isopropyl alcohol in the liquid phase has been examined. It is established that both the specific heat capacity of the material of the nanoparticles and structural changes of the base fluid around the nanoparticles are main factors that determine a decrease of the specific isobaric heat capacity of isopropyl alcohol. It was shown that the excess molar volume and excess molar isobaric heat capacity are determined by properties of the interfacial phase of structurally oriented isopropyl alcohol molecules on the surface of nanoparticles. A new three-phase model for prediction the molar isobaric heat capacity of nanofluids is proposed. To predict caloric properties of nanofluids the proposed model requires only data for the molar volume of the investigated samples.